Integrate torchgen exception boundary with ExecuTorch (#8321)

Pull Request resolved: https://github.com/pytorch/executorch/pull/7546

As of #7746, we build with exceptions by default, so we just need to use them.

ghstack-source-id: 265190625
@exported-using-ghexport

Differential Revision: [D67904052](https://our.internmc.facebook.com/intern/diff/D67904052/)

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Co-authored-by: Github Executorch <github_executorch@arm.com>